Thalamic projections from the whisker-sensitive regions of the spinal trigeminal complex in the rat

One of the most salient features of primary vibrissal afferents is their sensitivity to the direction in which the vibrissae move. Directional sensitivity is also well conserved in brainstem, thalamic, and cortical neurons of the lemniscal pathway, indicating that this property plays a key role in the organization of the vibrissal system. Here, we show that directional tuning is also a fundamental feature of second-order interpolaris neurons that give rise to the paralemniscal pathway. Quantitative assessment of responses to vibrissa deflection revealed an anisotropic organization of receptive fields with regard to topography, response magnitude, and the degree of angular tuning. Responses evoked by all vibrissae within the receptive field of each cell exhibited a high consistency of direction preference, but a striking difference in angular tuning preference was found among cells that reside in the rostral and caudal divisions of the interpolaris nucleus. Although in caudal interpolaris vectors of angular preference pointed in all directions, in rostral interpolaris virtually all vectors pointed upward, revealing a strong preference for this direction. Control experiments showed that the upward bias did not rely on a preferential innervation of rostral cells by upwardly tuned primary vibrissa afferents, nor did it rely on a direction-selective recruitment of feedforward inhibition. We thus propose that the upward preference bias of rostral cells, which project to the posterior group of the thalamus, emerges from use-dependent synaptic processes that relate to the kinematics of whisking.

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Angular Tuning Bias of Vibrissa-Responsive Cells in the Paralemniscal Pathway

Furuta

Nakamura²,

Deschênes³

2006

“…Brains were postfixed for 2 h, cryoprotected in 30% sucrose, and cut at 70 m on a freezing microtome. Sections were processed for cytochrome oxidase (CO) and Neurobiotin histochemistry according to standard protocols that were described in detail previously (Veinante et al, 2000).…”

Section: Methodsmentioning

confidence: 99%

“…Previous studies have shown that individual barreloids are composed of core and tail compartments, which receive vibrissal input from the principal trigeminal nucleus (PrV) and the caudal segment of the trigeminal interpolar nucleus (SpVic), respectively (Pierret et al, 2000;Veinante et al, 2000). In addition, several anatomical studies have pointed out to a functional specialization of the dorsalmost part of the barreloids that abuts Po (hereinafter referred to as the head of the barreloids).…”

Section: Introductionmentioning

confidence: 99%

A New Thalamic Pathway of Vibrissal Information Modulated by the Motor Cortex

Urbain¹,

Deschênes²

2007

Three ascending pathways of information processing have been identified so far in the vibrissal system of rodents. In the ventral posterior medial nucleus of the thalamus, two of these pathways convey information through the core and tail of barrel-associated structures, called barreloids. The other pathway transits through the posterior group nucleus. The present study provides anatomical and electrophysiological evidence for the existence of an additional pathway that passes through the head of the barreloids. This pathway arises from multiwhisker-responsive cells in the principal trigeminal nucleus and differs from the classic lemniscal pathway, in that constituent thalamic cells have multiwhisker receptive field and receive corticothalamic input from lamina 6 of the vibrissa motor cortex. It is suggested that this pathway might be involved in relaying signals encoding phase of whisker motion during free whisking.

“…Anatomically, POm receives inputs from brainstem afferents that fulfill the morphological criteria of driver inputs (Veinante et al, 2000). Physiologically, Chiaia et al (1991) showed that electrically stimulating the trigeminal nucleus principalis or the subnucleus interpolaris in the brainstem generates action potentials with similar onset latencies in the VPM and POm, suggesting that both nuclei respond in a similar manner to brainstem inputs.…”

Section: Introductionmentioning

confidence: 99%

Reducing the Uncertainty: Gating of Peripheral Inputs by Zona Incerta

Trageser

Keller²

2004

155

152

Sensory inputs are relayed to the neocortex by "first-order" thalamic nuclei, the responses of which are determined by ascending inputs from peripheral receptors. In contrast, "higher-order" thalamic nuclei respond poorly to peripheral inputs, and their responses are thought to be determined by descending cortical inputs. We tested this hypothesis by recording from neurons in the higher-order somatosensory posterior medial (POm) nucleus of narcotized rats. As reported previously, POm neurons responded to whisker stimuli with long-latency (median, 27 msec) and low-magnitude responses, consistent with cortically driven responses. However, when we suppressed inhibitory inputs from the subthalamic nucleus zona incerta (ZI), POm responses were of significantly higher magnitude and shorter latency, with many POm neurons responding at latencies consistent with ascending driving inputs from trigeminal nuclei. Our data suggest that POm comprises two neuronal populations: one population is driven by both peripheral and cortical inputs, and the second population responds only to cortical inputs. These findings demonstrate that ZI gates peripheral inputs to POm, enabling it to function both as a first-order and higher-order nucleus. Because ZI innervates all higher-order nuclei, this gating mechanism may exert similar regulation of thalamic processing in other sensory systems.